The gamma chains of the high affinity IgE receptor are also a subunit of other receptors. They are part of the low affinity IgE receptor in NK cells and macrophages and part of the T cell antigen receptor in some subsets of T cells. We have isolated and analysed the regulatory regions of the gamma chain gene and found that two major elements containing Alu sequences control the expression of this gene. One of these elements bind similar nuclear factors in basophils and T cells, while the other element bind to nuclear factors which are different in basophils and T cells. We also have isolated the gene for the human ` chain and we are in the process of characterizing the regulatory elements of this gene. In addition, we are studying the tissue distribution of expression of the ` gene and the possible factors involved in the regulation of the alpha gene in various types of cells.